The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group


wctomb - convert a wide-character code to a character


#include <stdlib.h>

int wctomb(char *
s, wchar_t wchar);


[CX] [Option Start] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard. [Option End]

The wctomb() function shall determine the number of bytes needed to represent the character corresponding to the wide-character code whose value is wchar (including any change in the shift state). It shall store the character representation (possibly multiple bytes and any special bytes to change shift state) in the array object pointed to by s (if s is not a null pointer). At most {MB_CUR_MAX} bytes shall be stored. If wchar is 0, a null byte shall be stored, preceded by any shift sequence needed to restore the initial shift state, and wctomb() shall be left in the initial shift state.

[CX] [Option Start] The behavior of this function is affected by the LC_CTYPE category of the current locale. For a state-dependent encoding, this function shall be placed into its initial state by a call for which its character pointer argument, s, is a null pointer. Subsequent calls with s as other than a null pointer shall cause the internal state of the function to be altered as necessary. A call with s as a null pointer shall cause this function to return a non-zero value if encodings have state dependency, and 0 otherwise. Changing the LC_CTYPE category causes the shift state of this function to be unspecified.

The wctomb() function need not be thread-safe. [Option End]

The implementation shall behave as if no function defined in this volume of POSIX.1-2008 calls wctomb().


If s is a null pointer, wctomb() shall return a non-zero or 0 value, if character encodings, respectively, do or do not have state-dependent encodings. If s is not a null pointer, wctomb() shall return -1 if the value of wchar does not correspond to a valid character, or return the number of bytes that constitute the character corresponding to the value of wchar.

In no case shall the value returned be greater than the value of the {MB_CUR_MAX} macro.


The wctomb() function shall fail if:

[CX] [Option Start] An invalid wide-character code is detected. [Option End]

The following sections are informative.










mblen, mbtowc, mbstowcs, wcstombs

XBD <stdlib.h>


First released in Issue 4. Derived from the ANSI C standard.

Issue 6

Extensions beyond the ISO C standard are marked.

A note indicating that this function need not be reentrant is added to the DESCRIPTION.

Issue 7

Austin Group Interpretations 1003.1-2001 #156 and #170 are applied.

End of informative text.


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